Waste heat recovery systems seek to recover and repurpose heat that is produced as a result of various processes, such as internal combustion engine-generated heat in an automobile. In the automotive industry, thermoelectric generators (TEGs) are employed in vehicles to harvest this waste heat and convert the waste heat to electricity for use by other components of the vehicles.
In a typical thermoelectric generator for waste heat recovery from exhaust gas, heat exchangers are passive metal chambers with baffles and/or fins through which the exhaust gas or coolant flow. The temperature of the hot and cold side heat exchangers is determined by the heat load of the exhaust gas and the efficiency of the cooling circuit, the heat capacity of the system components, and the efficiency of the heat recovery process. If there are high levels of excess heat, such as when the engine is under heavy load, the heat recovered could cause the temperature of the waste heat recovery system to exceed its operating limits. Typically, a bypass valve is incorporated into the system so that the exhaust gas can be shunted around the thermoelectric generator to prevent overheating; however, this can lead to a lower overall efficiency of the waste heat recovery when the operating temperatures of the hot and cold side heat exchangers in the system are not optimized.
Accordingly, it is desirable to provide temperature stability of the hot and cold side heat exchangers of the thermoelectric generators at optimum operating temperatures in order to maximize electrical power generation efficiency, as well as lengthen the useful life of the thermoelectric modules.